;;
;; Copyright (c) 2010, Justin Grant <justin at imagine27 dot com>
;; All rights reserved.

;; Redistribution and use in source and binary forms, with or without modification
;; are permitted provided that the following conditions are met:

;; Redistributions of source code must retain the above copyright notice, this list
;; of conditions and the following disclaimer.
;; Redistributions in binary form must reproduce the above copyright notice, this
;; list of conditions and the following disclaimer in the documentation and/or
;; other materials provided with the distribution.
;; Neither the name of the <ORGANIZATION> nor the names of its contributors may be
;; used to endorse or promote products derived from this software without specific
;; prior written permission.
;;
;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
;; ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
;; DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
;; ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
;; (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
;; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
;; THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE
;; EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
;;


(defn reverse-ll-slow [lst]
  (letfn [(reverse-ll
           [rlst lst]
           (if (= (count lst) 0)
             rlst
             (recur (cons (first lst) rlst) (rest lst))))]
    (reverse-ll '() lst)))

;; (let [nums (range 1 1e6)] (time (take 5 (reverse-ll-slow nums) nil)))
;; "Elapsed time: 4.0474063827E7 msecs"


(defn reverse-ll-fast [lst]
  (reduce (fn [rlst item] (cons item rlst)) '() lst))

;;(let [nums (range 1 1e6)] (time (take 5 (reverse-ll-fast nums))))
;; "Elapsed time: 698.739 msecs"


;; one-liner
;;(let [nums (range 1 1e6)] 
;;   (time (take 5 (reduce (fn [rlst item] (cons item rlst)) '() nums))))
